The present invention relates generally to signal acquisition and display apparatuses, such as an oscilloscope, and more particularly to a method and apparatus for providing a data envelope for an acquired signal.
Signal acquisition and display apparatuses, such as oscilloscopes, are well known devices that receive an input signal, and sample and display the signal in the time domain. Often, it is desirable to define an envelope, or highest and lowest amplitudes, for all time values of a signal. This envelope can then be used for various calculations, and to interpolate amplitudes for time values in which no sample of the original signal was actually taken.
Traditionally, generation of these envelopes have involved the acquisition of multiple waveforms, and the determination of min/max amplitudes for each sampled time value of the multiple waveforms. These min/max values are generated over a large number of signal acquisitions. Such a system is set forth in U.S. Pat. No. 6,201,527 issued to Dobyns. In this patent, a signal is acquired, and min/max data pairs are stored for each of a plurality of sequential samples. An envelope function is generated utilizing min/max pairs from a predetermined number of signal samples. Thus, as is shown in FIG. 3 thereof, the envelope is related not only to the most recently acquired signal sample, but a past number of signal samples.
Inherent in the '527 patent is that the acquired signal samples be somewhat consistent so that the generated envelope is indicative of overall structure and amplitude of the acquired signal. However, a signal sample including an error, or some other anomaly would generate an envelope that was at first indicative of the min/max values generated by the anomaly. Thereafter, the min/max values from the anomaly would move beyond the predetermined number of samples used to generate the envelope, and information about the anomaly would be lost.
Therefore, it would be beneficial to provide an improved method and apparatus that cured the defects of the prior art.